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Stumped

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WillG

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What I have/know
RV-3B
O320 -E2D
46 hrs since OH
Sent out existing Cylinders for OH
New Pistons,Rings Exhaust /Intake Valves
Ex. Int seats etc. - springs as needed.
#3 is the issues - NO not to hot, runs to cold
MGL - EGT/CHT new gauge w/new probes
Switched probes no change.
Example -
@ run up all cylinders 300 + - 10 degrees
After landing/ taxi back - about same
65 degree day
The issue - After climb out & temps stabilize
#3 falls to 200 others, 290, 275, 300 for an example
So on the ground without flying air, if you will
all is good.
I'm not using the # 3 washer or bump out cowl fix.
Any ideas , RV-3 cowl is tight, don't think that is related.
My new thought is soft intake spring??
 
What are the EGT readings doing?

Couple random WAG thoughts on possible suspects are extremely lean #3, massive air leak.

Intake valve not opening correctly-----bad lifter on #3 intake?? Wrong pushrod length?
 
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EGT are all pretty consistent, nothing stands out.
I did not add this is a Carb engine.
I did check comp press cold - 72-74
And scope looks good, of course only 46 hrs
I did replace most pushrods because length was not in spec.
Don't think it has a intake leak or it would run hot
 
A big intake leak should make a bigger difference at higher vacuum operation, like idle. I'm assuming your cruise is relatively fast speed, throttle mostly open?

Try adding carb heat at cruise... does that cause the CHT's to get closer together? [this can improve mixture distribution in a carb'd plane]
Can you dump the data from the engine monitor and upload to a free Saavy account, then give us images of CHT / EGT / RPM? Fuel Flow if you have it....
 
blaplante said:
A big intake leak should make a bigger difference at higher vacuum operation, like idle. I'm assuming your cruise is relatively fast speed, throttle mostly open?

Try adding carb heat at cruise... does that cause the CHT's to get closer together? [this can improve mixture distribution in a carb'd plane]
Can you dump the data from the engine monitor and upload to a free Saavy account, then give us images of CHT / EGT / RPM? Fuel Flow if you have it....
Click to expand...
The example I used was @ 2300 RPM for cruise - #3 dropped down to about 200 degrees other were near 300 + - this it what i am seeing.
they all seem a little low, but my concern is how low only #3 is at cruise.
And I did try the carb heat and one mag on one off check and saw no increase or decrease in #3 CHT
Although not a cruise RPM, but at Run -up check of 1800 rpm there is no drop from from #3
I just don't think the cylinder is using all the fuel available at higher RPM from soft springs or wrong push-rod length.
I can confirm PR length is correct, replace intake gasket and replace the intake springs and see if any of those work.
??
 
WillG said:
The example I used was @ 2300 RPM for cruise - #3 dropped down to about 200 degrees other were near 300 + - this it what i am seeing.
they all seem a little low, but my concern is how low only #3 is at cruise.
And I did try the carb heat and one mag on one off check and saw no increase or decrease in #3 CHT
Although not a cruise RPM, but at Run -up check of 1800 rpm there is no drop from from #3
I just don't think the cylinder is using all the fuel available at higher RPM from soft springs or wrong push-rod length.
I can confirm PR length is correct, replace intake gasket and replace the intake springs and see if any of those work.
??
Click to expand...
Have you tried a different set of plugs in #3? When you did the "one mag on one mag off" check at cruise RPM, did you do this with each mag? Is the ignition harness in good condition?

If the pushrod length is within spec then I don't think that could affect the opening, however a worn cam lobe would.
 
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PaulvS said:
Have you tried a different set of plugs in #3? When you did the "one mag on one mag off" check at cruise RPM, did you do this with each mag? Is the ignition harness in good condition?
Click to expand...
PaulvS said:
Have you tried a different set of plugs in #3? When you did the "one mag on one mag off" check at cruise RPM, did you do this with each mag? Is the ignition harness in good condition?
Click to expand...
Paul,
The Ignition is - two Slick Mags new rebuilt, with the auto plug harness conversion -only 46 hrs.at this point.
I did replace the plugs with new earlier when trying to figure the issue.
Yes, Right mag on - Left off -- Left on - Right off
There is no noticeable miss, with the exception of the normal slight RPM drop going from two mags to one
The lifter followers with cam are new, the hydro units are exchange for tested OH units, they say.
All I can come-up with is to replace - $ , or confirm , Hydro units, P. Rods length , Springs & Intake gasket are good.
Will
 
WillG said:
Paul,
The Ignition is - two Slick Mags new rebuilt, with the auto plug harness conversion -only 46 hrs.at this point.
I did replace the plugs with new earlier when trying to figure the issue.
Yes, Right mag on - Left off -- Left on - Right off
There is no noticeable miss, with the exception of the normal slight RPM drop going from two mags to one
The lifter followers with cam are new, the hydro units are exchange for tested OH units, they say.
All I can come-up with is to replace - $ , or confirm , Hydro units, P. Rods length , Springs & Intake gasket are good.
Will
Click to expand...
Hopefully one of the real engine gurus on here may chime in. Suggest changing the post title to "Stumped by LOW cht on #3" and move it to the Traditional Engines forum, may get a few more bites that way.
 
2300 at 4000' DAlt will be about 57% power. Not exactly pushing it. I'm assuming a fixed pitch prop.
What happens when you push it up - say 2500 rpm?
 
blaplante said:
2300 at 4000' DAlt will be about 57% power. Not exactly pushing it. I'm assuming a fixed pitch prop.
What happens when you push it up - say 2500 rpm?
Click to expand...
Normally I only see 2500 rpm at T. O. climb out - and #3 CHT temp is the lowest.
I've paid more attention the temperature differential amount in cruise.
Not that I can't check that at full throttle.
Yes, fixed pitched and carburetor.
I don't see this @ run-up @ 1800 RPM
 
PaulvS said:
Hopefully one of the real engine gurus on here may chime in. Suggest changing the post title to "Stumped by LOW cht on #3" and move it to the Traditional Engines forum, may get a few more bites that way.
Click to expand...
I agree, I posted this in the wrong category, don't know how to move it.
 
Have you verified that the CHT probes are in the location that you think they are? You can verify with a heat gun or even popping them out and holding it in your hand.. should move the numbers enough to verify they are the correct position.
 
You can verify lifter, cam lobe and pushrods with a dial indicator on the rockers. Turn your motor over by hand and verify lift and duration. Compare to another cylinder and the measurements you come up with should be pretty close. If not then you might have to get your hands dirty and dig a little deeper.
danny
 
I would switch cht probes and wiring between #1 and #3. That would check the entire sensing circuit by comparison. One thing to mention is that without all the sensing available, you would not think this engine has a problem. Its making power, running smooth and other wise without symptoms. If it were installed back in the Cessna 172 it originally came from, which didn't even have a CHT gauge, you would be happy with it. To me, if the cylinder was running that cool due to not making as much power as the others than you would feel some roughness. You obviously have very exceptional cooling in your nacelle, or you have erroneous readings on all cylinders (which is a real possibility with such low CHT on all cylinders). I would be thinking along those lines until I eliminated them. If the sensing circuit passes the test of swapping probes and wiring, I would think about subbing in another CHT gauge with the existing still functioning and comparing them. If the sensing circuit proves to be perfectly accurate, then I would maybe try reducing the cooling air inlet or outlet slightly and see if that helps. Good Luck, Mahlon
 
Taltruda said:
Have you verified that the CHT probes are in the location that you think they are? You can verify with a heat gun or even popping them out and holding it in your hand.. should move the numbers enough to verify they are the correct position.
Click to expand...
Yes, I confirmed Cyl. # Probe to gauge location & boiling water test.
 
danny said:
You can verify lifter, cam lobe and pushrods with a dial indicator on the rockers. Turn your motor over by hand and verify lift and duration. Compare to another cylinder and the measurements you come up with should be pretty close. If not then you might have to get your hands dirty and dig a little deeper.
danny
Click to expand...
Good Idea.
 
WillG said:
Good Idea.
Click to expand...
mahlon_r said:
I would switch cht probes and wiring between #1 and #3. That would check the entire sensing circuit by comparison. One thing to mention is that without all the sensing available, you would not think this engine has a problem. Its making power, running smooth and other wise without symptoms. If it were installed back in the Cessna 172 it originally came from, which didn't even have a CHT gauge, you would be happy with it. To me, if the cylinder was running that cool due to not making as much power as the others than you would feel some roughness. You obviously have very exceptional cooling in your nacelle, or you have erroneous readings on all cylinders (which is a real possibility with such low CHT on all cylinders). I would be thinking along those lines until I eliminated them. If the sensing circuit passes the test of swapping probes and wiring, I would think about subbing in another CHT gauge with the existing still functioning and comparing them. If the sensing circuit proves to be perfectly accurate, then I would maybe try reducing the cooling air inlet or outlet slightly and see if that helps. Good Luck, Mahlon
Click to expand...
Good point, I will go over all probe wiring and confirm, and subbing in another CHT gauge temporary is a good idea.
 
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